1. Field of the Invention
The invention relates to an image processing method, and more particularly to a method for scaling up an image.
2. Description of the Related Art
The video technology has been widely used in various electrical products. Generally speaking, when the compression/decompression modules utilize the standard video encoder/decoder, such as JPEG, MPEG, MPEG-2, MPEG-4, H.263, H.264, and the like, to process the image frame, the modules have to store the image data in the memory temporarily or permanently for the processing necessity.
However, in the system having ultra-large frame and ultra-high frame rates, the frame consumes a lot memory space and the system bus bandwidth, and thus tends to increase the system loading. For example, in a HDTV (High-Definition Television), each frame needs the memory space for 1920*1088*1.5=3.13 Mbytes, wherein 1920*1088 is the frame resolution.
Because the resolution of the frame of HDTV can reach 1920×1088, two problems should be considered. The first problem is that the memory required by the system is too large. The second problem is that the bandwidth consumed by the data transmission of the system is too large. In order to reduce the consumption of the bandwidth and the memory space without changing the architecture of the conventional decoder, the frame data should be compressed before the data is written in the memory or inputted to the bus, and returned to the original condition after the data is read or before the data is inputted to the micro-controller. Hence, the memory space and the transmission bandwidth can be reduced by using the compression unit and decompression unit.
FIG. 1 is a diagram showing that four points are compressed into one point. Some simple compression methods in the pixel domain will be described in the following.
1. Average of four points: four points in a 2×2 block of FIG. 1 are averaged into a point as the compression value of four points. That is,
      y    ⁡          (              m        ,        n            )        =            1      4        ⁢                  ∑                  k          =          0                1            ⁢                        ∑                      h            =            0                    1                ⁢                              x            ⁡                          (                                                i                  +                  h                                ,                                  j                  +                  k                                            )                                .                    
2. Take the point at the upper-left corner: the upper-left point of the block is directly taken as the compression value of the four points. That is,y(m,n)=x(i,j).
If the compression value is going to be returned to the original shape, one of the following methods may be applied.
1. Duplicate into four points: the four points in the block use duplicated average.
2. Bilinear interpolation: take a linear interpolation of two adjacent points to obtain the value of the point between the two adjacent points.
It is known in the art that the frame compression and decompression methods greatly influence the frame quality. The designer needs to choose a proper method so as to prevent the frame quality from deterioration.